1. Field of the Invention
This invention relates generally to an apparatus for preventing transmission shock in a vehicle equipped with an automatic transmission powered by an inverter driven motor. More particularly it relates to an apparatus for preventing transmission shock in a vehicle equipped with an automatic transmission which can reliably prevent transmission shock during a shift.
2. Description of the Related Art
Conventionally, in an automatic transmission equipped vehicles that run on the power of an engine via a transmission, it has been important to reduce transmission shock in order to improve ride comfort, therefore, various apparatuses for preventing transmission shock have been developed.
For example, in the apparatus for preventing transmission shock disclosed in Japanese Patent Publication No. 4-67058, the ignition timing of an engine is retarded to reduce the engine torque at the time of a transmission shift.
FIG. 3 is a timing chart showing the action of the apparatus for preventing transmission shock in a vehicle with an automatic transmission as described in the above reference.
In FIG. 3, (a) is the shift command C that shifts the automatic transmission up from second gear into the third gear, (b) is the input "rpm" Ri of the automatic transmission as it gradually reduces due to the shift into third gear, and (c) is the ignition timing Tp that is retarded when the transmission is shifted to third gear.
The action of this prior apparatus for preventing transmission shock in an automatic transmission equipped vehicle described in the above reference will be clarified with the following description in accordance with FIG. 3.
For example, when the shift command C to shift from second gear into third gear is generated at time t1, the gear change from the ratio G2 of second gear into the ratio G3 of third gear begins at time t2 after fixed response delay time.
At this time, by shifting the gear ratios, a difference between the input rpm Ri of the automatic transmission and a value (referred to as "divided output rpm value" hereinafter) obtained by dividing the output shaft rpm Ro by the gear ratio after shifting in response to the shift command C is generated to generate transmission shock. Accordingly, in order to reduce this transmission shock, the ignition timing Tp is retarded as shown in FIG. 3 so as to reduce the output torque of the engine.
Then, at time t3 when the difference between the input rpm Ri of the automatic transmission and the divided output rpm value decreases to no more than a fixed value, the ignition timing Tp starts to return to normal ignition timing, and at time t4, the shifting is terminated and the output torque is returned to nomal.
Even, in electric power type automatic transmission equipped vehicles powered by an inverter driven motor, similar methods of reducing the transmission shock by reducing the motor torque output during transmission shifting as in the engine powered type vehicle above are being used.
However, in this case, there is a problem in that the transmission shock is generated by the energy accumulated by the moment of inertia of the motor.
As mentioned above, the conventional apparatus for preventing transmission shock in an automatic transmission equipped vehicle has a problem in that it is difficult to prevent the transmission shock, since it is generated in proportion to the energy accumulated at the moment of inertia of the motor when shifting.